A water tank containing a seaweed filter is preventing old lead and silver mines from polluting a river near Aberystwyth.

Early results from a trial of the new system shows that toxic materials are no longer entering the River Clarach.

Up to a kilo of zinc a day is being extracted in the £1.4m project.

Ceredigion has 38 of the 50 most infected metal mine sites in Wales, according to the Environment Agency.

The Bioman (Bioabsorption of Metals from Abandoned Mine Sites) has been working near Aberystwyth.

Field trials of the system began at a mine last Friday, led by Dr Bill Perkins of Aberystwyth University's geography and earth sciences department.

I am very, very pleased with the way the field trials are going

Dr Bill Perkins

He said that high levels on zinc, lead and cadmium, which is used to make rechargeable batteries, had been extracted from water flowing from the mine.

Up to one kilo of zinc per day is being extracted along with up to five grammes of lead and up to one gram of cadmium.

"We chose the mine near Penparcau (near Aberystwyth) because it had the highest level of toxic material," said Dr Perkins.

"The Bioman has been absorbing high levels of zinc, lead and cadmium. Zinc is particularly detrimental to all aquatic life."

He added: "I am very, very pleased with the way the field trials are going.

"Over the next few weeks we'll be developing the size and capacity of the trial."

Encourage tourists

Dr Perkins explained that water had been flowing out of the mines into streams and then into rivers.

Bioman was developed by an international team of scientists with the backing of a £1.4m European Commission grant.

The team from Aberystwyth has been working with scientists from Sheffield University and the University of Bologna in Italy.

The prototype Bioman unit consists of an average-sized loft cold water tank. Inside is a large tea bag-like structure filled with dealginated seaweed, a by-product of an industrial process to make food additives from seaweed.

It is treating one litre of mine water per minute.

In December last year, Ceredigion, which is home to around 100 former lead and silver mines, was awarded a £450,000 grant.

The 'Spirit of the Miners' project aims to breathe life into the uplands of Ceredigion.

Officials hope the legacy of the industry will be used to encourage tourists to the region.